Fiber optic connectors are used to terminate the ends of fiber optic cables. There are many different fiber optic connector types. Example types of fiber optic connectors include FC-type, SC-type, ST-type and D4-type.
FIG. 1 shows a typical connector 10. A ferrule 12 is located inside the connector 10. The ferrule 12 is a relatively long, thin cylinder preferably made of a material such as ceramic. Other materials such as metal or plastic can also be used to make the ferrule 12. The ferrule 12 defines a central opening 14 sized to receive a fiber 16 of a given cladding diameter. An epoxy is typically placed into the opening 14 prior to inserting the fiber 16 to hold the fiber 16 in place. The ferrule 12 functions to align and center the fiber 16, as well as to protect it from damage.
Referring still to FIG. 1, the ferrule 12 is supported within a connector body 18 typically made of a material such as metal or plastic. The connector body 18 is typically bonded to fiber optic cable 20 (e.g., the cable 20 can include a reinforcing layer made of a material such as Kevlar that is affixed to the connector 18). A strain relief boot 22 protects the junction between the connector 18 and the cable 20. Two connectors are preferably interconnected through the use of an adapter 24. Adapter 24 includes a sleeve 26 sized to receive the ferrules of the connectors desired to be connected. For example, ferrule 12 of connector 10 is inserted into a first end 28 of the sleeve 26, while a ferrule (not shown) of a connector desired to be connected to the connector 10 is inserted into a second end 30 of the sleeve 26. As so inserted, the ends of the ferrules abut one another within the sleeve 26 such that their corresponding fibers are held in alignment with one another.
It is desirable to minimize the loss of signals passing through the fiber. Parameters for evaluating the performance of a connector include insertion loss and return loss. Insertion loss is the measurement of the amount of power that is transferred through a coupling from an input fiber to an output fiber. Return loss is the measurement of the amount of power that is reflected back into the input fiber. To enhance signal quality and therefore optimize insertion/return loss, it is desirable to polish an end face 13 of the ferrule 12. During the polishing process, the ferrule 12 is commonly held in a fixture, and the end 13 is pressed against an oscillating and rotating disk. Frequently, the end 13 is polished to form a spherical polished surface oriented along a plane that is perpendicular with respect to the longitudinal axis of the fiber 16. However, for some applications, the end 13 is polished to form a spherical surface aligned at an oblique angle with respect to the longitudinal axis of the fiber 13.
FIG. 2 is a block diagram showing the steps of a convention ferrule polishing technique for providing a rounded ferrule tip. During a first polishing step 70, a hackle of the fiber and residue epoxy are removed from the ferrule tip typically by a hand-sanding process or automated system such as an epoxy removal machine. After the hackle and epoxy have been removed, the tip of the ferrule is machine polished using two or more polishing films (e.g., of varying coarseness) so as to more precisely form an apex and radius into the tip of the ferrule (see step 72). Next, the tip of the ferrule is machine polished with a final polish film as indicated by step 74. During the polishing process, an index layer is formed at the tip of the fiber within the ferrule. The index layer has undesirable optical properties. Thus, at final step 76, the tip of the ferrule is polished with a cerium oxide film causing the fiber to be recessed slightly into the ferrule a distance sufficient to remove the index layer. For some applications, the tip is recessed prior to the final polish, as disclosed, for example, in U.S. patent application Ser. No. 10/071,856, filed Feb. 8, 2002, which is hereby incorporated by reference.